It's a bug so prevalent that I can consistently recreate it. It crashes even more often if a weapon used to trigger it has any AoE component to it. Two most consistent triggers are Magelocks and Heavy Melee weapons (so far)
#Killing Momentum Crashing
bright halo
nocturne jay
If you want to report a bug, please use the forum. There's a post in the announcements explaining how. As for my experience, I've never had killing momentum crash a game, even with AoE components. So you should provide a lot more detail about the exact weapons, enchants, and situations that created this. (On the forum) especially if it is repeatable.